Advances in Wine Fermentation

Vineyard-mediated factors are still operative in spontaneous and commercial fermentations shaping the vinification microbial community and affecting the antioxidant and anticancer properties of wines

The grapevine and vinification microbiota have a strong influence on the characteristics of the produced wine. Currently we have a good understanding of the role of vineyard-associated factors, like cultivar, vintage and terroir in shaping the grapevine microbiota. Notwithstanding, their endurance along the vinification process remains unknown. Thus, the main objective of our study was to determine how these factors influence (a) microbial succession during fermentation (i.e., bacterial and fungal) and (b) the antioxidant, antimutagenic and anticancer potential of the produced wines. These were evaluated under different vinification strategies (i.e., spontaneous V1, spontaneous with preservatives V2, commercial V3), employed at near full-scale level by local wineries, for two cultivars (Roditis and Sideritis), two terroir types, and two vintages. Cultivar and vintage were strong and persistent determinants of the vinification microbiota, unlike terroir whose effect became weaker from the vineyard, and early fermentation stages, where non-Saccharomyces yeasts, filamentous fungi (i.e., Aureobasidium, Cladosporium, Lachancea, Alternaria, Aspergillus, Torulaspora) and acetic acid bacteria (AAB) (Gluconobacter, Acetobacter, Komagataeibacter) dominated, to late fermentation stages where Saccharomyces and Oenococcus become prevalent. Besides vineyard-mediated factors, the vinification process employed was the strongest determinant of the fungal community compared to the bacterial community were effects varied per cultivar. Vintage and vinification type were the strongest determinants of the antioxidant, antimutagenic and anticancer potential of the produced wines. Further analysis identified significant positive correlations between members of the vinification microbiota like the yeasts Torulaspora debrueckii and Lachancea quebecensis with the anticancer and the antioxidant properties of wines in both cultivars. These findings could be exploited towards a microbiota-modulated vinification process to produce high-quality wines with desirable properties and enhanced regional identity.

Metabolic Fingerprinting of Muscat of Alexandria Grape Musts during Industrial Alcoholic Fermentation Using HS-SPME and Liquid Injection with TMS Derivatization GC-MS Methods

Muscat of Alexandria is one of the most aromatic grape cultivars, with a characteristic floral and fruity aroma, producing popular appellation of origin wines. The winemaking process is a critical factor contributing to the quality of the final product, so the aim of this work was to study metabolomic changes during the fermentation of grape musts at the industrial level from 11 tanks, 2 vintages, and 3 wineries of Limnos Island. A Headspace Solid-Phase Microextraction (HS-SPME) and a liquid injection with Trimethylsilyl (TMS) derivatization Gas Chromatography-Mass Spectrometry (GC-MS) methods were applied for the profiling of the main volatile and non-volatile polar metabolites originating from grapes or produced during winemaking, resulting in the identification of 109 and 69 metabolites, respectively. Multivariate statistical analysis models revealed the differentiation between the four examined time points during fermentation, and the most statistically significant metabolites were investigated by biomarker assessment, while their trends were presented with boxplots. Whilst the majority of compounds (ethyl esters, alcohols, acids, aldehydes, sugar alcohols) showed an upward trend, fermentable sugars, amino acids, and C6-compounds were decreased. Terpenes presented stable behavior, with the exception of terpenols, which were increased at the beginning and were then decreased after the 5th day of fermentation.

The Life of Saccharomyces and Non-Saccharomyces Yeasts in Drinking Wine

Drinking wine is a processed beverage that offers high nutritional and health benefits. It is produced from grape must, which undergoes fermentation by yeasts (and sometimes lactic acid bacteria) to create a product that is highly appreciated by consumers worldwide. However, if only one type of yeast, specifically Saccharomyces cerevisiae, was used in the fermentation process, the resulting wine would lack aroma and flavor and may be rejected by consumers. To produce wine with a desirable taste and aroma, non-Saccharomyces yeasts are necessary. These yeasts contribute volatile aromatic compounds that significantly impact the wine's final taste. They promote the release of primary aromatic compounds through a sequential hydrolysis mechanism involving several glycosidases unique to these yeasts. This review will discuss the unique characteristics of these yeasts (Schizosaccharomyces pombe, Pichia kluyveri, Torulaspora delbrueckii, Wickerhamomyces anomalus, Metschnikowia pulcherrima, Hanseniaspora vineae, Lachancea thermotolerans, Candida stellata, and others) and their impact on wine fermentations and co-fermentations. Their existence and the metabolites they produce enhance the complexity of wine flavor, resulting in a more enjoyable drinking experience.

Estimation of Sugar Content in Wine Grapes via In Situ VNIR-SWIR Point Spectroscopy Using Explainable Artificial Intelligence Techniques

Spectroscopy is a widely used technique that can contribute to food quality assessment in a simple and inexpensive way. Especially in grape production, the visible and near infrared (VNIR) and the short-wave infrared (SWIR) regions are of great interest, and they may be utilized for both fruit monitoring and quality control at all stages of maturity. The aim of this work was the quantitative estimation of the wine grape ripeness, for four different grape varieties, by using a highly accurate contact probe spectrometer that covers the entire VNIR-SWIR spectrum (350-2500 nm). The four varieties under examination were Chardonnay, Malagouzia, Sauvignon-Blanc, and Syrah and all the samples were collected over the 2020 and 2021 harvest and pre-harvest phenological stages (corresponding to stages 81 through 89 of the BBCH scale) from the vineyard of Ktima Gerovassiliou located in Northern Greece. All measurements were performed in situ and a refractometer was used to measure the total soluble solids content (°Brix) of the grapes, providing the ground truth data. After the development of the grape spectra library, four different machine learning algorithms, namely Partial Least Squares regression (PLS), Random Forest regression, Support Vector Regression (SVR), and Convolutional Neural Networks (CNN), coupled with several pre-treatment methods were applied for the prediction of the °Brix content from the VNIR-SWIR hyperspectral data. The performance of the different models was evaluated using a cross-validation strategy with three metrics, namely the coefficient of the determination (R2), the root mean square error (RMSE), and the ratio of performance to interquartile distance (RPIQ). High accuracy was achieved for Malagouzia, Sauvignon-Blanc, and Syrah from the best models developed using the CNN learning algorithm (R2>0.8, RPIQ≥4), while a good fit was attained for the Chardonnay variety from SVR (R2=0.63, RMSE=2.10, RPIQ=2.24), proving that by using a portable spectrometer the in situ estimation of the wine grape maturity could be provided. The proposed methodology could be a valuable tool for wine producers making real-time decisions on harvest time and with a non-destructive way.

Study of Fungal Communities in Dry Red Wine Fermentation in Linfen Appellation, Shanxi

In this study, the fermentation mash of Cabernet Sauvignon, Cabernet Franc, and Matheran from Linfen, Shanxi Province, was sequenced using the Illumina MiSeq high-throughput sequencing platform to analyze the structural diversity of fungal communities in different samples. The results showed that a total of 10 phyla, 125 families, and 187 genera were detected in the nine samples of this study. The main fungal phyla were Ascomycota, Basidiomycota, and Mortierellomycota. The main fungal genera are Hanseniaspora, Mortierella, Sclerotinia, Aureobasidium, Saccharomyces, Aspergillus, Clavulina, Candida, etc. Hanseniaspora was the dominant genus in the pre-fermentation stage, accounting for more than 70%; Saccharomyces was the dominant genus in the middle and late fermentation stage, accounting for more than 75% in the middle fermentation stage and up to 90% in the late fermentation stage. This study provides a theoretical basis for monitoring and optimizing winemaking processes and introducing wine grape varieties in the Linfen region of Shanxi.

Native Non-Saccharomyces Yeasts as a Tool to Produce Distinctive and Diverse Tamjanika Grape Wines

The enological potential of two previously characterized indigenous yeast isolates, Hanseniaspora uvarum S-2 and Candida famata WB-1, in pure and sequential inoculation with commercial yeast Saccharomyces cerevisiae QA23 were analyzed in industrial-scale vinification of the grape variety Tamjanika. Their contribution to the quality and aroma profile was investigated by quantifying volatile compounds and wine sensory evaluation. Both yeast isolates were able to complete alcoholic fermentation, to reduce ethanol concentration up to 1.06% v/v (in monoculture) in comparation to S. cerevisiae QA23, and to enhance aroma and sensory profile. Based on calculated odor activity values (OAV), p-cymene, ethyl hexanoate, ethyl octanoate, and ethyl decanoate were the major aroma volatile compounds in all Tamjanika wine samples. Analyzed yeast strains significantly affected relative contribution of volatile compounds and can be considered responsible for the differences and uniqueness of the obtained wine samples. Besides confirmation of good enological and fermentative characteristics, selected isolates can be characterized as high ester-producing strains with potential to enhance the floral and fruity aromas of wine. The present study represents a further step toward the use of indigenous yeast isolates at industrial-scale fermentation in order to ensure the regional signature of Tamjanika wine.